Experimental data suggests that cultured rat mesangial cells possess characteristics of immune effector cells that could potentially contribute to the structural and functional derangements observed in glomerulonephritis. The recent observation that cultured rat mesangial cells release an interleukin-1-line cytokine, mesangial cell-derived thymocyte activating factor (MC-TAF), is consistent with this hypothesis. Interleukin-1 (IL-1) is a true hormone produced by monocytes and macrophages during inflammation, which has multiple bioactivities. Pertinent to this proposal is the considerable evidence that IL-1 acts locally at sites of injury and that cells other than monocytes or macrophages are capable of producing IL-1-like cytokines. This suggests locally produced IL-1-like cytokines may be a mediate local inflammation. The effects of IL-1 on glomerular function are unknown; IL-1 is mitogenic for both human and rat cultured mesangial cells. However, the effects of IL-1 on other target cells suggests that it could have profound effects on glomerular function in glomerulonephritis. Since other factors in crude or partially purified mesangial-cell supernatants could cause thymocyte proliferation, we propose experiments to characterized MC-TAF as an interleukin-1 molecule, to assess its regulation in cultured rat mesangial cells, and finally to assess its expression in experimental models of glomerulonephritis. Ribonucleic nucleic acid (RNA) will be extracted from proliferating, mesangial cells, and dot blot and Northern hybridizations will then be performed using a murine IL- 1 cDNA to determine if mesangial cells express RNA transcripts with significant homology to macrophage IL-1. Mesangial cell RNA will be translated in vitro and assayed for IL-1 activity. In situ hybridization technology will be used to verify the cell of origin of the IL-1 transcripts. The effects of agents (with know effects on mesangial cells) on the expression of mesangial cell IL- 1 will be studied by measuring MC-TAF activity and by assessing the transcription of IL-1 mRNA. To assess IL-1 expression in glomerular disease, we will measure IL-1 transcripts in rats and mice with experimental glomerulonephritis using RNA extracted from cortical and medullary tissue and isolated glomeruli. We will also perform in situ hybridization on cryostat kidney sections to anatomically localize the site of IL-1 transcription.